All of the commonly practiced processes for fabricating three-dimensional objects have disadvantages. For example, the mechanical removal of material to form such objects involves much energy, time and processing; the chemical machining to form such objects has depth limitations and the incapability of making complex shapes; and the thermal molding requires expensive molds; it is very inflexible and it takes much time and energy.
Several methods and apparatus have been developed for the production of three-dimensional objects by irradiation of photopolymers that cross-link and solidify upon irradiation. Forming three-dimensional objects by solidifying each point individually can be accomplished by scanning the whole volume of the object point by point with intersecting beams, as described, for example, in U.S. Pat. Nos. 4,041,476 and 4,288,861. However, such methods are very complex and expensive. The forming of three-dimensional objects by building-up successive extremely thin laminae of the solidified photopolymer is described in U.S. Pat. No. 4,575,330. The method involves many production steps due to the large number of laminae required. As a result the system can be time consuming and complex. There also are other drawbacks such as shrinkage distortion of the open irradiated surface.
An article "A New Method of Three Dimensional Micromachining" published in the September 1985 issue of Mechanical Engineering describes the fabrication of three-dimensional objects in a single irradiation process using a mask modulating the intensity of radiation across the irradiated surface to vary depth of solidification. However, only objects with a single layer of cavities which are limited in geometry can be produced. More complex objects, and objects of larger thickness, can only be made by forming separate slices and later attaching them together. To provide a good surface for joining the slices together, the irradiated surface is covered with a rigid glass plate to which the solidified polymer adheres. However, the glass causes the polymer surface which it contacts to lose some of its cross-linking capability which makes it difficult to join the slices together.
In my article "Sculpting with Light" published Mar. 6, 1986 in Machine Design, I have described the use of a radiation source that modulates the amount of radiation across the irradited surface to vary depths of solidification, the formulae for calculating the required light intensity for solidification, and related matter. That article is incorporated by reference herein.
Three-dimensional objects of various geometries are widely used everywhere in final products, prototypes and models. A large portion of such objects could be made of photopolymers by photosolidification if there were a suitable apparatus and method of producing these objects which resulted in dramatic reductions in cost and time and improvements in accuracy and performance characteristics.